1) Field of the Invention
The invention relates to a device for producing a product gas from biomass, comprising a reactor which is delimited by a base part and reactor walls, which reactor walls comprise a circumferential wall and an upper wall, which reactor comprises:                a supply opening for the supplying of biomass,        at least one riser for the chemical conversion of supplied biomass to at least a product gas, which riser is attached within the circumferential wall and comprises an upper end and a lower end, and also        a discharge opening for the discharging of the product gas.        
2) Description of Related Art
A device of this type is known. The biomass supplied to the riser usually comprises 80% by weight of volatile constituents and 20% by weight of substantially solid carbon or char. Heating said biomass supplied to the riser to an appropriate temperature in an atmosphere having a low oxygen content or containing no oxygen causes pyrolysis and gasification in the riser. Said appropriate temperature in the riser is usually greater than 800° C., for example between 850 and 900° C.
Pyrolysis of the volatile constituents produces a product gas. The product gas is, for example, a gas mixture comprising CO, H2, CH4 and optionally higher hydrocarbons. After further treatment, this combustible product gas is suitable to serve as a fuel. The char present in the biomass will, in conjunction with the low gasification rate, gasify in the riser merely to a limited extent. The char is therefore usually burned separately in the reactor. Moreover, pyrolysis and gasification can result in the release of various undesired substances such as tar.
During start-up of the installation, the temperature rises within a relatively short time from chamber temperature to pyrolysis and gasification temperature. The riser is therefore subject to considerable thermal expansion. This can result in damage to the riser, such as the formation of cracks.